There is an ongoing effort to improve fuel mileage in motor vehicles. In the last half century, fuel mileage improvements from internal combustion engines have most often resulted from volumetric efficiency improvements (i.e.: increased peak horsepower per unit volume of cylinder displacement) rather than thermal efficiency improvements. Fuel mileage gains have come by way of increased strength and horsepower of engines, allowing smaller displacement engines to be installed into larger vehicles, where the engines are tasked to operate within a more thermally efficient segment of their operating range. Fuel mileage improvements can become tougher to achieve as small displacement engines more routinely populate large vehicles.
Atkinson engines, which are found in some of today's most fuel efficient cars, achieve improved thermal efficiency through an expansion process which reduces volumetric efficiency and which expels less heat energy to the exhaust duct than do equivalently powered Otto engines. HCCI engine development programs, now popular in laboratories around the world, achieve improved thermal efficiency through a combustion process which reduces volumetric efficiency and which expels less heat energy to the exhaust duct than do equivalently powered Otto and Diesel engines. Atkinson and HCCI engines suggest some thermodynamic processes with reduced volumetric efficiency and cooler exhaust gas temperature can provide a pathway toward improved engine thermal efficiency and vehicle fuel economy.
Exhaust emissions aftertreatment devices in motor vehicles often require a high exhaust gas temperature to scrub pollutants from the exhaust stream. Some engines which combine high thermal efficiency with low volumetric efficiency will have unconventionally cool exhaust temperatures, rendering many conventional emissions aftertreatment devices inoperative. What is needed is an improved apparatus and method to prevent the formation of pollutants during the combustion reaction in an internal combustion engine, reducing the need for exhaust after treatment.